Micromechanical resonating devices and related methods

ABSTRACT

Micromechanical resonating devices, as well as related methods, are described herein. The resonating devices can include a micromechanical resonating structure, an actuation structure that actuates the resonating structure, and a detection structure that detects motion of the resonating structure.

RELATED APPLICATIONS

This application is a continuation of, and claims the benefit under 35U.S.C. §120 of, U.S. patent application Ser. No. 12/181,531 filed Jul.29, 2008 and entitled “Micromechanical Resonating Devices and RelatedMethods,” the entire contents of which is incorporated herein byreference.

FIELD OF INVENTION

The invention relates generally to micromechanical resonating devices,and more particularly, to tunable micromechanical resonating devices aswell as related methods.

BACKGROUND OF INVENTION

Tunable devices can be used for various applications such as performingsignal processing operations and functions. It is advantageous to havetunable devices because one can tune and/or calibrate a device toaccount for any manufacturing glitches while implementing a design on achip or to provide a user the flexibility to adjust, if desired, theoperating conditions of a device. For example, a filter can be tuned toadjust the pass band spectral range. In another example, an amplifiercan be tuned for achieving a particular gain.

One method of tuning devices is by tuning the capacitance. For example,basic designs of filters include LR (inductor-resistor) and RC(resistor-capacitor) filters, and by tuning the capacitance, one cantune the filter. A tunable capacitance is also useful in several otherdevices such as charge capacitors, tunable antennas, and mobile phones.

Several methods currently exist for tuning capacitors. However many ofthe methods require excessive circuit size, complex circuitry, and/orresult in increased loss, and low Q-factors. Furthermore, tradeoffsbetween capacitance tuning, impedance matching, and a high Q factor makedesigns for tunable capacitive designs complicated.

SUMMARY OF INVENTION

Micromechanical resonating devices, as well as related methods, aredescribed herein.

According to one aspect, a micromechanical device is provided. Themicromechanical device comprises a mechanical resonating structure andan actuation structure constructed and arranged to actuate theresonating structure. The micromechanical device further comprises adetection structure constructed and arranged to detect motion of theresonating structure. An actuation gap is defined between a firstportion of the resonating structure and a portion of the actuationstructure, and a detection gap is defined between a second portion ofthe resonating structure and a portion of the detection structure. Atleast one of the actuation structure and the detection structure isconstructed and arranged to move relative to the resonating structure torespectively tune the actuation gap and/or the detection gap.

According to another aspect, a micromechanical device is provided. Thedevice comprises a mechanical resonating structure including a suspendedresonating portion defined between a first end and a second end. Themicromechanical device further comprises an actuation structureconstructed and arranged to actuate the resonating structure. Theactuation structure includes a suspended actuation portion definedbetween a third end and a fourth end. The micromechanical device furthercomprises a detection structure constructed and arranged to detectmotion of the resonating structure. The detection structure includes asuspended detection portion defined between a fifth and a sixth end.

According to another aspect, a micromechanical device is provided. Thedevice comprises a capacitive structure comprising a suspended firstportion and a suspended second portion separated from the first portionby a distance. At least one of the first portion and the second portionis designed to actuate in response to an applied bias to change thedistance. The micromechanical device further comprises a mechanicalresonating structure located, at least in part, between the firstportion and the second portion.

According to another aspect, a timing oscillator is provided. The timingoscillator comprises a mechanical resonating structure including a majorelement and a minor element coupled to the major element and a drivecircuit designed to provide an input signal to the mechanical resonatingstructure. The timing oscillator further comprises a compensationcircuit coupled to the mechanical resonating structure, an actuationstructure constructed and arranged to actuate the mechanical resonatingstructure, and a detection structure constructed and arranged to detectmotion of the mechanical resonating structure. An actuation gap isdefined between a portion of the mechanical resonating structure and aportion of the actuation structure. A detection gap is defined between aportion of the mechanical resonating structure and a portion of thedetection structure. At least one of the actuation structure and thedetection structure is constructed and arranged to move relative to themechanical resonating structure to respectively tune the actuation gapand/or the detection gap.

According to another aspect, a method of operating a micromechanicaldevice is provided. The method comprises providing a micromechanicaldevice. The micromechanical device includes a mechanical resonatingstructure, an actuation structure constructed and arranged to actuatethe resonating structure, and a detection structure constructed andarranged to detect motion of the resonating structure. An actuation gapis defined between a portion of the resonating structure and a portionof the actuation structure. A detection gap is defined between a portionof the resonating structure and a portion of the detection structure.The method further comprises moving the actuation structure and/or thedetection structure relative to the resonating structure to respectivelytune the actuation gap and/or detection gap. The method furthercomprises actuating the resonating structure.

Other aspects, embodiments and features of the invention will becomeapparent from the following detailed description of the invention whenconsidered in conjunction with the accompanying drawings. Theaccompanying figures are schematic and are not intended to be drawn toscale. In the figures, each identical, or substantially similarcomponent that is illustrated in various figures is represented by asingle numeral or notation. For purposes of clarity, not every componentis labeled in every figure. Nor is every component of each embodiment ofthe invention shown where illustration is not necessary to allow thoseof ordinary skill in the art to understand the invention. All patentapplications and patents incorporated herein by reference areincorporated by reference in their entirety. In case of conflict, thepresent specification, including definitions, will control.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a micromechanical resonating deviceaccording to an embodiment of the present invention.

FIG. 2 shows a diagram of a tunable micromechanical resonating devicewith no applied biasing according to an embodiment of the presentinvention.

FIG. 3 shows a diagram of a tunable micromechanical resonating devicewith applied biasing according to an embodiment of the presentinvention.

FIG. 4 shows a tunable micromechanical resonating device with aresonating structure having major and minor elements according to anembodiment of the present invention.

FIG. 5 shows a block diagram of a generic circuit according to anembodiment of the present invention.

FIG. 6 shows a tunable micromechanical resonating device with a circularresonating structure according to an embodiment of the presentinvention.

FIG. 7 shows a timing oscillator including a tunable micromechanicalresonating device according to an embodiment of the present invention.

DETAILED DESCRIPTION

Micromechanical resonating devices, as well as related methods, aredescribed herein. The resonating devices can include a micromechanicalresonating structure, an actuation structure that actuates theresonating structure, and a detection structure that detects motion ofthe resonating structure. The actuation structure can be separated fromthe resonating structure by one gap (e.g., actuation gap) and thedetection structure can be separated from the resonating structure byanother gap (e.g., detection gap). As described further below, byapplying a bias (i.e., voltage, current) to one or more of thestructures, the actuation and/or detection gap(s) may be changed. Inthese cases, as described further below, the applied bias enables tuningof the gap distance. For example, the gap(s) may be decreased comparedto an original gap distance to increase the effective capacitancebetween the actuation structure and resonating structure and/or betweenthe detection structure and resonating structure. Increasing theeffective capacitance can minimize signal losses within the device,amongst other advantages, which can enhance performance.

FIG. 1 shows a block diagram of a micromechanical resonating device 200according to an embodiment of the invention. The device can include anactuation structure 202, a resonating structure 204, and a detectionstructure 206. As described further below, the device can be designed toallow several characteristics (i.e., capacitive gap(s), resonantfrequency) to be tuned. The tunability of the characteristics makes suchdevices very useful and attractive in numerous applications andcircuits, such as filters, timing oscillators, and charge pumps. Thedevices may include one or more active and/or passive circuitcomponents, either as discrete components, an integrated circuit, or anyother suitable form, as the various aspects of the invention are notlimited to any particular implementation.

The actuation structure 202 is the driving mechanism of the device. Thatis, the actuation structure is used to drive the resonating structure byactuating (i.e., moving) the resonating structure to vibrate at adesired frequency. In general, any suitable actuation structure andassociated excitation technique may be used to drive the resonatingstructure 204. Examples of suitable actuation structures are describedfurther below, including micromechanical actuation structures (e.g.,that include one or more feature having a dimension of less than 100microns). In some cases, the actuation structure uses a capacitive(i.e., electrostatic) excitation technique to actuate the resonatingstructure. However, it should be understood that other excitationtechniques may be used in certain embodiments such as mechanical,electromagnetic, piezoelectric or thermal.

In the embodiments shown, the resonating structure 204 is amicromechanical resonator. Micromechanical resonators are physicalstructures that are designed to vibrate at high frequencies. Suitablemicromechanical resonators have been described, for example, inInternational Publication No. WO 2006/083482, U.S. patent applicationSer. No. 12/028,327, filed Feb. 8, 2008, and in U.S. patent applicationSer. No. 12/142,254, filed Jun. 19, 2008, and published as U.S. PatentPublication No. 2009/0243747 A1, which are incorporated herein byreference in their entireties. In general, a variety of differentresonator designs may be used for the resonating structure. For example,the structures may include beams (e.g., suspended beams), platforms andthe like; the structures can be comb-shaped, circular, rectangular,square, or dome-shaped, as described further below.

The detection structure 206 detects motion of the resonating structure.In general any suitable structure and associated detection technique maybe used. In some embodiments, the detection structure comprises amicromechanical structure. Examples are described further below. In someembodiments, the detection structure may have a structure similar to theactuation structure. In other embodiments, the detection structure andthe actuation structure can be the same structure. That is, the devicemay include a single structure that functions as both the actuationstructure and the detection structure. For example, in the device ofFIG. 2, structure 202 may function as a detection structure as well asthe actuation structure.

According to some embodiments, the detection structure uses a capacitive(i.e., electrostatic) technique to sense the motion of the resonatingstructure. However, it should be understood that other detectiontechniques may be used in certain embodiments such as mechanical,electromagnetic, piezoelectric or thermal.

The detection structure can have sensors capable of detecting operatingconditions of the device and/or of measuring characteristics of anoutput signal. For example, the detection structure may measure thefrequency of the signal generated by the resonating structure. Thedetection structure may also be able to sense the gap between theresonating structure and the detection structure and/or between theactuation structure and the resonating structure. The detectionstructure may also be able to measure the current across a portion inthe actuation and/or detection structures.

Sensors can be integrated into the detection structure or can beconnected to the detection structure using any suitable means. Forexample, a sensor and/or sensing circuitry can be attached to thedetection circuit as an external component. The sensors, after obtaininga measurement, can provide feedback to the actuation structure or adrive circuit to modify, if needed, the performance of the resonatingstructure. For example, using the feedback mechanism, a measuredfrequency of the resonating structure can be tuned to another frequency,if needed, by adjusting the bias supplied to the actuation structure.

In the illustrative embodiments, the actuation structure can beseparated from the resonating structure by an actuation gap 214, and thedetection structure can be separated from the resonating structure by adetection gap 212. The actuation gap is generally defined between aportion 208 of the actuation structure and a portion 216 of theresonating structure; and, the detection gap is defined between aportion 210 of the detection structure and a portion 218 of theresonating structure. The actuation and/or detection gaps do not have tobe constant along the length of the resonating structure. For example,the distance between different parts of the resonating structure and theactuation structure and/or detection structure may vary from one part ofthe resonating structure to another. The actuation and/or detection gapsmay also be static or dynamic during use. For example, in some cases, agap may be dynamic and vary over time and, in other cases, a gap may bestatic and may remain substantially constant over time.

According to some embodiments, portions 208, 210, 216 and 218 aresufficiently electrically conductive to form respective capacitorsbetween portions 208 and 216, and between portions 210 and 218. In suchembodiments, the actuator gap and detection gap may be referred to ascapacitive gaps.

The portions may be formed of a suitably electrically conductivematerial such as a metal or doped semiconductor. The portions may beformed of a different material (e.g., in the form of a coating) thanother parts of the actuation, resonating and detection structures. Thatis, portion 208 may be formed of a first material, while other parts ofthe actuation structure may be formed of a different material. However,in some embodiments, the portions are formed of the same material asother parts of the actuation, resonating and detection structures. Also,it should be understood that the portions may not extend across theentire surface area of the actuation structure, resonating structure,and/or detection structure. That is, the portions may be a localizedregion on the actuation structure, resonating structure and/or detectionstructure.

In some embodiments, actuation gap 214 and/or detection gap 212 arevariable and can be tuned. By tuning, it is meant that the gap(s) can bevaried by controlling an input parameter. For example, a bias (i.e.,voltage, current) may be applied to one or more of the actuation,detection and resonating structures to tune the gap. When a bias (220,222) is applied to the actuation and/or detection structure, acapacitance across the actuation gap between portions 208 and 216 can bemodified. The capacitance can be determined as a function of the area ofportions (208, 216) and the gap between the portions, and thepermittivity of the medium between the portions. Varying the bias, forexample, can cause one of the portions to move and the capacitance tochange. For example, the gap between the portions may be decreased andthe capacitance may be increased. For example, portion 208 (andassociated parts of the actuation structure) may be moved closer toportion 216 (and associated parts of the resonating structure). Inaddition, the resonating frequency of the resonating structure can betuned by varying this bias and changing the effective capacitancebetween the two portions.

In some embodiments, the actuation and/or detection gap can be tunedinternally because input parameters that control the tuning of thegap(s) can be adjusted internally. For example, the feedback mechanismdescribed above can automatically tune the gap(s) internally. In otherembodiments, the actuation and/or detection gap can be tuned externally.For example, an applied bias can be adjusted externally by a user. Theapplied bias used to tune the gap(s) can, in come embodiments, bedifferent then the bias used to control other aspects of themicromechanical resonating device. For example, the tuning bias may bedifferent than the bias used to drive the resonating structure.

Other methods of tuning the gap(s) include stress storing andthermomechanical heating. For example, when a current flows acrossportion 208, the portion can get heated and expand. Expansion of theportion can lead to a reduction of the gap between the resonatingstructure and the actuation structure and/or detection structure. Ingeneral, any suitable method known to one of ordinary skill in the artmay be used.

In some embodiments, the actuation gap and/or detection gap is reducedby between 1% and 99%; in some embodiments by between 1% and 33% itsoriginal value; and in other embodiments by between 1% and 50%. Typicalgap distances, after reduction, are between 0.01 microns and 100microns; or, between 1 microns and 100 microns; or, between 0.01 micronsand 0.1 microns. Typical original gap distances, before reduction, arebetween 0.1 microns and 100 microns; or, between 0.3 microns and 10microns.

FIG. 2 shows a resonating structure 218 situated between a actuationstructure 308 and a detection structure 302 according to someembodiments. In the illustrative embodiment, the actuation structureincludes a suspended element 314 and a fixed element 306; and, thedetection structure includes a suspended element 316 and a fixed element304. As described further below, the suspended elements are movable, forexample, in response to electrostatic forces. As illustrated in FIG. 2,these elements may include a and/or comb-shaped structure. Suchcomb-shaped structures are well known in the art. The comb structurescan be separated by a distance and may have interleaved fingerelectrodes capable of being activated when a voltage is applied.

Though the illustrative embodiments show both the actuation structureand the detection structure as including a fixed element and a suspendedelement, it should be understood that a variety of differentconfigurations are possible. For example, in some embodiments, theactuation structure and/or detection structure may include two suspendedelements. In other embodiments, only one of the actuation structure orthe detection structure may include such elements. In some cases, theactuation and/or detection structures may have different designs thatare not based on fixed and/or suspended elements. It should also beunderstood that the resonating structure may include a suspendedelement, as shown in the figures.

In FIG. 2, the suspended element, for example, is fixed at ends 318.Similarly, in this embodiment, the detection structure includes asuspended element 316 held fixed at ends 320. Also, as shown, thesuspended resonating structure 310 is fixed at ends 322. The ends candefine and/or limit the location and movement of the suspendedactuation, detection, and/or resonating structures.

Furthermore, motion limiting elements 312 may be used to limit themotion of the actuation structure and/or the detection structure towardthe resonating structure thereby limiting the respective gaps asdescribed further below. For example, the motion limiting elements canbe placed between the resonating structure and the actuation structureand/or between the resonating structure and the detection structure tolimit the movement of the actuation structure and the movement of thedetection structure. In general, any number of motion limiting elementsmay be used in any suitable configuration to limit the motion of thestructures.

According to some embodiments, the motion limiting elements can ensurevariable gaps 212 and 214 are not reduced too significantly (e.g., bymore than 66% of the original (i.e., steady-state gap) to preventinadvertent contact or pull-in between the resonating structure and theactuation and/or detection structures. Thus, the motion limitingelements can enhance the stability of the device.

In general, the motion limiting elements may have any suitable design.In some embodiments, the motion limiting elements are features thatlimit movement by physical contact with the appropriate structure (e.g.,actuation structure, detection structure). For example, part of thesuspended elements 314, 316 may physically contact the motion limitingelements to limit their motion.

FIG. 3 shows the device of FIG. 2 after tuning of the actuation anddetection gaps. It should be understood that, in some embodiments, onlyone of the actuation and detection gaps is tuned. For example, in theseembodiments, the actuation gap may be tuned; or, the detection gap maybe tuned.

The gaps may be tuned by application of a bias (i.e., voltage, current).For example, a voltage may be applied to actuation structure and/or theresonating structure and/or the detection structure. When a bias (220,222) is applied to the activation and detection structures, as shown inFIG. 3, the respective distances between the suspended elements 314, 316and stationary elements 304, 306 of the actuation and detectionstructures may be reduced. In such cases, the suspended element can movetowards the stationary element. If both elements are suspended andmovable, then both structures may move towards each other.

The applied bias creates a difference in voltage between the actuationstructure and the resonating structure and/or between the detectionstructure and the resonating structure. The applied bias can also causea current to flow in portions 208 and 210. The voltage difference andcurrent flow can cause portions 314 and 316 to move as shown in FIG. 3.The amount of movement depends on several factors including the amountof applied bias. In general, any suitable voltage or current may beapplied to the actuation structure. The movement can be towards theresonating structure or away from the resonating structure, though inmost embodiments, movement that decreases the actuation and detectiongaps is preferred.

The current flow in portions 314 and 316 can create capacitivestructures, as described above. The capacitive structures can be createdbetween portion 216 of the resonating structure and portion 208 of theactuation structure and/or between portion 218 of the resonatingstructure and portion 210 of the detection structure. Actuation ormovement of portion 314 (and 208) and/or portion 316 (and 210) due tothe applied bias also affects the capacitance between portion 216 of theresonating structure and portion 208 of the actuation structure and/orthe capacitance between portion 218 of the resonating structure andportion 210 of the detection structure. Other properties that can beinfluenced by the movement of portions 314 and 316 include the resonancefrequency, the Q-factor, the effective impedance and associated networklosses. Thus, by carefully monitoring and manipulating the actuationstructure, one can control the capacitance, the resonance frequency, theeffective impedance and associated network losses of the device. Forexample, if the effective impedance is too high, an applied voltage maybe adjusted to lower the effective device impedance. In another example,the current supplied by the actuation structure may be adjusted toensure the output signal produced by the resonator has a certainfrequency.

When devices described herein are used, in some embodiments, theactuation and/or detection gap is tuned (e.g., reduced), as describedabove. In conjunction with the tuning, the resonating structure can beactuated by the actuation structure so that the resonating structureresonates at a desired frequency. The resonating structure is actuatedby the electrostatic forces generated from the applied bias. In someembodiments, the resonating structure resonates primarily in a planeperpendicular to the actuation gap and/or the detection gap.

According to some embodiments, as shown in FIG. 4, a resonatingstructure 502 includes multiple minor elements 504 coupled to a majorelement 506. The minor elements are in the form of cantilever beams andthe major element is in the form of a doubly-clamped beam which extendsbetween two supports. Suitable excitation provided by the actuationstructure vibrates the minor elements at a high frequency. Vibration ofthe minor elements influences the major element to vibrate at a highfrequency but with a larger amplitude than that of the individual minorelements. Mechanical vibration of the major element may be converted toan electrical output signal which, for example, may be furtherprocessed. The frequency produced by the resonating structure can, forexample, vary from a few KHz up to 10 GHz, depending on the design andapplication. Other suitable mechanical resonator designs may be used,including designs with different arrangements of major and minorelements.

Major and minor element dimensions are selected, in part, based on thedesired performance including the desired frequency range of inputand/or output signals associated with the device. Suitable dimensionshave been described in International Publication No. WO 2006/083482which is incorporated herein by reference above. It should also beunderstood that the major and/or minor elements may have any suitableshape and that the devices are not limited to beam-shaped elements.Other suitable shapes have been described in International PublicationNo. WO 2006/083482.

In some embodiments, the minor elements have dimensions in the nanoscaleand are thus capable of vibrating at fast speeds producing resonantfrequencies at significantly high frequencies (e.g., 0.1-10 GHz). Themajor element coupled to the minor elements then begins to vibrate at afrequency similar to the resonant frequency of the minor elements. Eachminor element contributes vibrational energy to the major element whichenables the major element to vibrate at a higher amplitude than possiblewith only a single nanoscale element. The vibration of the major elementcan produce an electrical signal, for example, in the gigahertz range(or higher) with sufficient strength to be detected, transmitted, and/orfurther processed enabling devices to be used in many desirableapplications including wireless communications.

In general, the minor elements have at least one smaller dimension(e.g., length, thickness, width) than the major element. Minor elementscan have a shorter length than the major element. The minor elements mayhave nanoscale (i.e., less than 1 micron) dimensions. In someembodiments, at least one of the dimensions is less than 1 micron; and,in some embodiments, the “large dimension” (i.e., the largest of thedimensions) is less than 1 micron. For example, minor elements may havea thickness and/or width of less than 1 micron (e.g., between 1 nm and 1micron). Minor elements may have a large dimension (e.g., length)between about 0.1 micron and 10 micron; between 0.1 micron and 1 micron;or, between 1 micron to 100 micron. The major element can have a widthand/or thickness of less than 10 micron (e.g., between 10 nm and 10micron). The major element may have a length of greater than 1 micron(e.g., between 1 micron and 100 micron); in some cases, the majorelement 21 has a length of greater than 10 micron (e.g., between 10micron and 500 micron). In some cases, the major element has a largedimension (e.g., length) of less than 500 micron. It should beunderstood that dimensions outside the above-noted ranges may also besuitable.

In general, the devices may be used in any suitable circuit for anysuitable application. For example, FIG. 5 illustrates an example of atypical signal processing circuit implemented on a chip having anysuitable substrate. The circuit 100 can be divided into an input network102, an output network 106, and a central network 104.

The central network can be a device as described herein. According tosome embodiments, the device may be tuned by applying the necessaryvoltage to produce an output signal at a desired frequency or a filterat a particular band while also matching the impedance between the inputnetwork and the central network and the impedance between the centralnetwork and the output network. This is a critical advantage in most RFand signal processing circuits since circuit mismatches can result indeteriorated performance due to losses. Typically impedances for thethree networks are designed at 50Ω; however this impedance value mayvary depending on the application. In certain cases, designers mayretain mismatches to achieve a particular design objective.

It should also be understood that the devices may have severalconfigurations and/or geometries. The geometry of the device caninclude, for example, any antenna type geometry, as well as beams,cantilevers, free-free bridges, free-clamped bridges, clamped-clampedbridges, discs, rings, prisms, cylinders, tubes, spheres, shells,springs, polygons, diaphragms and tori. FIG. 6, for example,illustrates, according to some embodiments, a resonating structure ofthe device having a circular geometry with the actuation and detectionstructures also having circular portions. Any of the mechanicalresonating structure and/or coupling elements may be formed either inwhole or in part of the same or different geometries. In addition,several different type geometrical structures may be coupled together toobtain particular resonance mode responses. It should be understood thatnot all embodiments include major and minor mechanical resonatingelements. Structures of portions are not limited to beam structures andmay be array structures, circular structures, and any other suitablestructure.

According to some embodiments, the devices can be integrated in tunablemeters, mass sensors, gyros, accelerometers, switches, andelectromagnetic fuel sensors. According to some embodiments, the devicescan be integrated in a timing oscillator. Timing oscillators can be usedin several devices including digital clocks, radios, computers,oscilloscopes, signal generators, and cell phones. The devices canprecisely generate clock signals, for example, as a reference frequencyto help synchronize other signals that are received, processed, ortransmitted by a device in which the timing oscillator is integrated in.Often times, multiple processes are run simultaneously on a device andthe execution of such processes rely on a clock signal that can begenerated by the devices.

The timing oscillator can include a micromechanical resonating device702, a drive circuit 704 coupled to the device, and a compensationcircuit 706 adapted to adjust an output signal of the timing oscillator.Suitable timing oscillators have been described, for example, in U.S.patent application Ser. No. 12/111,544, filed Apr. 29, 2008 andpublished as U.S. Patent Publication No. 2009/0267699 A1, which isincorporated herein by reference in its entirety. A gap-tuning circuit712 can be part of the drive circuit, as shown in FIG. 7, or thecompensation circuit, or can be external to the drive circuit and to thecompensation circuit but coupled to the resonating structure. Theactuation structure can be coupled to the drive circuit and thedetection structure can be coupled to the drive circuit and/or thecompensation circuit. In some embodiments, the timing oscillatorincludes a synthesizer 708 coupled to the compensation circuit 706. Thesynthesizer can be external of the timing oscillator or integrated intothe drive circuit. A Phase-Locked Loop (PLL) is an example of asynthesizer that can control the phase of a signal generated by thedevice. According to some embodiments, the synthesizer may comprise afilter, oscillator, or other signal processing devices well known to oneof skill in the art. For example, the synthesizer can include a phasedetector to minimize the difference between a signal generated by adrive circuit and a signal generated by a voltage-controlled oscillator(VCO). This process is repeated until the VCO's signal has a phase thatmatches the drive circuit's phase.

According to some embodiments, the output of the timing oscillator canbe coupled to a processing circuit 710. The processing circuit caninclude any type of circuit or device to process the signal generated bythe timing oscillator 700. For example, the processing circuit mayinclude filters, mixers, dividers, amplifiers, or other applicationspecific components and devices. A generated signal can be transmittedto other devices using a transmitter built into the processingcircuitry. Configurations and connections between the processingcircuitry, synthesizer, and the device may vary depending on the type ofapplication and generated signal desired.

As discussed earlier, tunable devices offer several advantages whenapplied in various circuits and designs. For example, a micromechanicalresonating device with a tunable capacitive gap can be used to tune thepass band of a filter, or to provide excellent control in matching themotional impedance of the resonating structure with the input and outputnetworks of a device. In other cases, the motional impedance of acircuit can be tuned to obtain a desired mismatch within a device.

Having thus described several embodiments of this invention, it is to beappreciated that various alterations, modifications, and improvementswill readily occur to those skilled in the art. Such alterations,modifications, and improvements are intended to be part of thisdisclosure, and are intended to be within the spirit and scope of theinvention. Accordingly, the foregoing description and drawings are byway of example only.

1. An apparatus, comprising: a suspended mechanical resonatingstructure; and a bias structure disposed proximate a first side of thesuspended mechanical resonating structure and separated from thesuspended mechanical resonating structure by a first gap, wherein thebias structure is configured to tune a resonance frequency of thesuspended mechanical resonating structure by applying a bias to thesuspended mechanical resonating structure.
 2. The apparatus of claim 1,wherein the bias structure is a first bias structure, and wherein theapparatus further comprises a second bias structure disposed proximate asecond side of the suspended mechanical resonating structure andseparated from the suspended mechanical resonating structure by a secondgap, wherein the first and second bias structures are configured incombination to tune the resonance frequency of the suspended mechanicalresonating structure
 3. The apparatus of claim 1, wherein the biasstructure comprises a comb structure.
 4. The apparatus of claim 3,wherein the comb structure comprises a first, movable portion and asecond, stationary portion.
 5. A method of operating a suspendedmechanical resonating structure, the method comprising: tuning anoperation frequency of the suspended mechanical resonating by applying abias to the suspended mechanical resonating structure using a first biasstructure separated from the suspended mechanical resonating structureby a first gap.
 6. The method of claim 5, further comprising applying abias to the suspended mechanical resonating structure using a secondbias structure separated from the suspended mechanical resonatingstructure by a second gap.
 7. The method of claim 5, wherein tuning theoperation frequency comprises adjusting a capacitance across the firstgap.
 8. The method of claim 5, wherein tuning the operation frequencycomprises adjusting a distance of the first gap.
 9. The method of claim5, further comprising measuring the operation frequency of the suspendedmechanical resonating structure, and wherein tuning the operationfrequency is performed in response to measuring the operation frequency.10. The method of claim 5, wherein the bias is a bias voltage.